The present invention relates to a harmonic speed changer for use in, particularly, an industrial machine such as an industrial robot and particularly, to such speed changer suitable for use in an articulation connecting the arms of an industrial robot.
A typical example of a conventional speed changer of this type for reducing an input rotational speed at a predetermined ratio to obtain a reduced output rotation will be described with reference to FIGS. 1 to 3, in which FIGS. 1 and 2 show a main portion of the harmonic speed changer in cross sections taken along an axis of the speed changer and a line perpendicular to the axis, respectively. As shown in these figures, an annular circular spline 1 is formed on an inner surface thereof with a gear 1a and a cylindrical flexible spline 2 is formed on an outer surface thereof with a gear 2a to be meshed with the gear 1a of the circular spline. In this case, assuming that the number of teeth of the circular spline gear 1a is (n+2), the number of teeth of the gear 2a of the flexible spline 2 is generally smaller than that of the gear 1a and may be n. Also, as is clear from FIG. 2, the flexible spline 2 takes in the form of a cylinder having a thin wall, as a whole, so that it can be resiliently deformed easily upon exertion of external force.
The conventional harmonic speed changer is further provided with a rotatable wave generator 4 having an ellipsoidal cross section. The flexible spline 2 is supported by a peripheral surface of the wave generator 4 so that the flexible spline gear 2a is resiliently deformed along the ellipse of the wave generator 4 such that only portions of the gear 2a of the flexible spline 2 which correspond to opposite ends of a long diameter portion of the wave generator 4 mesh with the circular spline gear 1a. The circular spline 1 is fixed to a utilization means by bolts extending through bolt holes 1b and an output shaft of the speed changer is fixed to the flexible spline 2 by bolts extending through bolt holes 2b.
An input shaft is inserted into the wave generator 4 through a support member 5 to transmit rotation of the input shaft to the wave generator 4. During one revolution of the wave generator 4, the gear 2a of the flexible spline 2 meshes with the gear 1a of the circular spline one by one causing -2/n revolutions of the flexible spline 2, while deforming along the outer configuration of the wave generator 4. That is, in the harmonic speed changer, a reduction rate of -2/n is achieved. The resultant reduced revolution is transmitted to the output shaft connected to the flexible spline 2.
FIG. 3 shows an application of such harmonic speed changer to a certain industrial device.
FIG. 3, the circular spline 1 is fixed to an edge portion of a cavity 6a of the device 6 by bolts 7. The flexible spline 2 and the wave generator 4 are arranged with respect to the circular spline 1 as shown and an input shaft 8 is inserted into the wave generator 4 through the shaft support member 5. The output shaft 9 is connected to an output side of the flexible spline 2 by means of bolts 10. The output shaft 9 is supported by the device 6 through a ball bearing 11 to prevent the output shaft 9 from moving eccentrically.
With the arrangement mentioned above, revolution of the input shaft 8 causes revolution of the output shaft 9 at reduction ratio of -2/n through the harmonic speed changer having the circular spline 1, the flexible spline 2 and the wave generator 4. When the flexible spline 2 and the circular spline 1 are such that gear 1a has teeth larger in number than the gear 2a of the flexible spline 2 by two, revolution speed of the flexible spline 2 is reduced by 2/n. The reduced revolution speed is transmitted through the output shaft 9 connected to the flexible spline 2 to another mechanism (not shown).
According to the harmonic speed changer mentioned above, the input shaft 8 of the wave generator 4 and the output shaft 9 of the flexible spline 2 must be arranged coaxially with each other. Therefore, when, for example, such harmonic speed changer is used in an articulation disposed between the arms of an industrial robot, various electrical wirings and/or hydraulic and/or oil pipings for controlling movement of the robot arms must be arranged outside of the harmonic speed changer, which means that it is necessary to provide a space large enough to arrange these wirings and/or pipings around the harmonic speed changer.